Investigations On Optical Properties Of The Micro/nano-Structures Mimicking Butterfly Wing Scales

Morpho butterflies constitute one of the most popular examples of structural colors in nature. The micro/nano structures of the wing scales in Morpho butterflies are responsible for the brilliant and iridescent blue coloration, with a major part ascribed to interference and diffraction of light. And the investigation on mechanisms of structural color has become an important aspect of bionics.In this thesis, experiments and simulations have been combined to investigate the optical properties of Morpho butterfly wing scales. Our two experimental systems have been improved to measure the reflection spectra of the micro/nano structure of Morpho butterfly wing scales. If some liquid is dropped on the upper surface of the scales, the color will vary from blue to green and then return back to blue. At the start of the liquid volatilization process, the reflection spectrum can remain constant for some time. As the liquid further volatilizes, the reflection spectrum exhibits a slight fluctuation at first, and then the peak reflectance increases dramatically while the peak wavelength decreases.The optical properties of Morpho butterfly wing scales were investigated by simulating models using rigorous coupled-wave analysis technique (RCWA). The simulation results show that the optical properties of the model mimicking butterfly wing scales depend strongly on the structural parameters, incidence angle and refractive index. The peak reflectance and the peak wavelength increase as the vertical periodic thickness increases. The peak reflectance decreases observably, while both of the bandwidth and the peak wavelength increase when the number of the vertical periods decreases. Increase of the horizontal periodic width causes a decrease of the peak reflectance and an increase of the peak wavelength, although the variations are small. The peak reflectance decreases distinctly and the peak wavelength increases as the ambient refractive index increases, which corresponds to the variation in ambient conditions.Furthermore, there is good agreement between the measurement and simulation results of the color variations of Morpho butterfly wing scales. However, the simulated spectrum will return to the original state if the liquid completely volatilizes, and the measured one will change as the number of times that the liquid is dropped increases. The cuticle material of the butterfly wing scales has been found to be destroyed as the effect of the liquid.This research benefits our understanding of the color variation mechanisms of the wing scales, and provides inspiration for further studies and applications. And it is helpful to the design, manufacture and applications of the micro/nano-biomimetic structures for gas detection.